给定一个字符串s只由小写字母的,任务是找到可以从给定的字符串去除ķ字符来获得最大的字典序字符串。
例子:
Input: s = “zyxedcba”, K=1
Output: zyxedcb
Explanation: The character with the smallest ASCII value from the given string is ‘a’.
Removal of ‘a’ generates the lexicographically largest possible string.
Input: s = “abcde”, K=2
Output: cde
方法:
这个想法是使用堆栈数据结构来解决问题。请按照以下步骤解决问题:
- 遍历字符串。
- 对于每个字符,检查它是否大于堆栈顶部的字符。如果发现为真,则在K > 0 时弹出栈顶元素。
- 将字符插入堆栈。
- 完成对字符串的遍历后,如果K > 0 ,则移除栈顶的 K 个元素。
- 最后,将字符存储在堆栈中作为答案。打印答案。
下面是上述方法的实现:
C++
// C++ Program to implement the
// above approach
#include
using namespace std;
string largestString(string num, int k)
{
// final result string
string ans = "";
for (auto i : num) {
// If the current char exceeds the
// character at the top of the stack
while (ans.length() && ans.back() < i
&& k > 0) {
// Remove from the end of the string
ans.pop_back();
// Decrease k for the removal
k--;
}
// Insert current character
ans.push_back(i);
}
// Perform remaining K deletions
// from the end of the string
while (ans.length() and k--) {
ans.pop_back();
}
// Return the string
return ans;
}
// Driver Code
int main()
{
string str = "zyxedcba";
int k = 1;
cout << largestString(str, k) << endl;
}
Java
// Java program to implement the
// above approach
class GFG{
static String largestString(String num, int k)
{
// Final result String
String ans = "";
for(char i : num.toCharArray())
{
// If the current char exceeds the
// character at the top of the stack
while (ans.length() > 0 &&
ans.charAt(ans.length() - 1) < i &&
k > 0)
{
// Remove from the end of the String
ans = ans.substring(0, ans.length() - 1);
// Decrease k for the removal
k--;
}
// Insert current character
ans += i;
}
// Perform remaining K deletions
// from the end of the String
while (ans.length() > 0 && k-- > 0)
{
ans = ans.substring(0, ans.length() - 1);
}
// Return the String
return ans;
}
// Driver Code
public static void main(String[] args)
{
String str = "zyxedcba";
int k = 1;
System.out.print(largestString(str, k) + "\n");
}
}
// This code is contributed by 29AjayKumar
Python3
# Python3 program to implement the
# above approach
def largestString(num, k):
# Final result string
ans = []
for i in range(len(num)):
# If the current char exceeds the
# character at the top of the stack
while(len(ans) and ans[-1] < num[i] and
k > 0):
# Remove from the end of the string
ans.pop()
# Decrease k for the removal
k -= 1
# Insert current character
ans.append(num[i])
# Perform remaining K deletions
# from the end of the string
while(len(ans) and k):
k -= 1
ans.pop()
# Return the string
return ans
# Driver code
str = "zyxedcba"
k = 1
print(*largestString(str, k), sep = "")
# This code is contributed by divyeshrabadiya07
C#
// C# program to implement the
// above approach
using System;
class GFG{
static String largestString(String num, int k)
{
// Final result String
String ans = "";
foreach(char i in num.ToCharArray())
{
// If the current char exceeds the
// character at the top of the stack
while (ans.Length > 0 &&
ans[ans.Length - 1] < i && k > 0)
{
// Remove from the end of the String
ans = ans.Substring(0, ans.Length - 1);
// Decrease k for the removal
k--;
}
// Insert current character
ans += i;
}
// Perform remaining K deletions
// from the end of the String
while (ans.Length > 0 && k-- > 0)
{
ans = ans.Substring(0, ans.Length - 1);
}
// Return the String
return ans;
}
// Driver Code
public static void Main(String[] args)
{
String str = "zyxedcba";
int k = 1;
Console.Write(largestString(str, k) + "\n");
}
}
// This code is contributed by 29AjayKumar
Javascript
输出:
zyxedcb
时间复杂度: O(N)
辅助空间: O(N)
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